The present invention generally relates to adhesive joints and, more particularly, to adhesive joints configured to resist degradation in a chemically-hostile environment.
Adhesive joints are widely used in industry to join components. In some applications, an additional requirement placed upon an adhesive joint is that it be resistant to degradation in a chemically-hostile environment. An example of a chemically-hostile environment is the ink storage and delivery system of an inkjet printer.
Inkjet printers have gained wide acceptance. Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes the paper. An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes referred to as “dot locations”, “dot positions”, or “pixels”. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more printheads, each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing and position for the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
The typical inkjet printhead (i.e., the silicon substrate, structures built on the substrate, and connections to the substrate) uses liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent). It has an array of precisely formed nozzles attached to a printhead substrate that incorporates an array of firing chambers which receive liquid ink from the ink reservoir. Each chamber has a thin-film resistor, known as an inkjet firing chamber resistor, located opposite the nozzle so ink can collect between it and the nozzle. The firing of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements. When electric printing pulses heat the inkjet firing chamber resistor, a small portion of the ink next to it vaporizes and ejects a drop of ink from the printhead. Properly arranged nozzles form a dot matrix pattern. Properly sequencing the operation of each nozzle causes characters or images to be printed upon the paper as the printhead moves past the paper.
The ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath the medium is moved forward the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of the signals, the desired print is obtained on the medium.
The printhead may include a flexible circuit tape having conductive traces formed thereon and have nozzles or orifices formed by Excimer laser ablation, for example. The resulting flexible circuit having orifices and conductive traces may then have mounted on it a substrate containing heating elements associated with each of the orifices. The conductive traces formed on the back surface of the flexible circuit are then connected to the electrodes on the substrate and provide energization signals for the heating elements. A barrier layer, which may be a separate layer or formed in the nozzle member itself, includes vaporization chambers, surrounding each orifice, and ink flow channels which provide fluid communication between an ink reservoir and the vaporization chambers.
Typically, the integrated nozzle and flexible circuit or tape circuit is sealed to a print cartridge. A nozzle member containing an array of orifices has a substrate, having heater elements formed thereon, affixed to a back surface of the flexible circuit. Each orifice in the flexible circuit is associated with a single heating element formed on the substrate. The back surface of the flexible circuit extends beyond the outer edges of the substrate. Ink is supplied from an ink reservoir to the orifices by a fluid channel within a barrier layer between the flexible circuit and the substrate. In either embodiment, the flexible circuit is adhesively sealed with respect to the print cartridge body by forming an ink seal, circumscribing the substrate, between the back surface of the flexible circuit and the body.
However, it has been determined that adhesive loses its adhesive qualities due to exposure to the ink. Over time ink concentration in the adhesive increases. Degradation in joint strength has been found to occur in direct proportion to the concentration of ink absorbed by the adhesive. Prior solutions to protecting adhesive joints from the effects of the ink include: providing protecting coatings that cover the joint; using adhesives that are more resistant to the effects of the ink; providing designs that lengthen the diffusion distance of the ink into the adhesive by modifying the joint design; and modifying the joint design to reduce stress. All of these solutions are expensive to implement and/or provide less than satisfactory results.
Thus, there remains a need to increase the life of adhesive joints in ink jet cartridges, and other applications, that may be implemented simply and cost effectively without requiring additional materials or changes in the existing materials.